Background and liquidity (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended	6 Months Ended
	Dec. 17, 2019	Jul. 22, 2019	Jul. 31, 2019	Jul. 31, 2020	Jan. 31, 2020	Jul. 31, 2019
Background And Liquidity [Line Items]
Proceeds from initial public offering				$ 0		$ 130,781
Deferred offering costs				$ 0		$ 3,930
Conversion of preferred stock into common stock and cancellation of redeemable preferred stock (in shares)					757,625
Number of months the company have sufficient to fund its operations				12 months
Common Stock
Background And Liquidity [Line Items]
Issuance of common stock in initial public offering, net of issuance costs (in shares)	7,762,500		7,812,500
Deferred offering costs	$ 1,047
Conversion of preferred stock into common stock and cancellation of redeemable preferred stock (in shares)		25,311,525	25,311,535
IPO
Background And Liquidity [Line Items]
Issuance of common stock in initial public offering, net of issuance costs (in shares)		7,812,500
Issue price per share (in dollars per share)		$ 18.00
Proceeds from initial public offering		$ 130,781
Underwriting discounts and commission		9,844
IPO | Common Stock
Background And Liquidity [Line Items]
Deferred offering costs		$ 6,412
IPO | Certain Selling Stockholders
Background And Liquidity [Line Items]
Issuance of common stock in initial public offering, net of issuance costs (in shares)		2,868,923